Complement dependent trapping of infectious HIV in human lymphoid tissues.

OBJECTIVES: HIV-1 bound extracellularly to follicular dendritic cells (FDC) in germinal centers (GC) of lymphoid tissues (LT) represents the largest viral reservoir in HIV-infected individuals; however there is no direct evidence as to whether HIV trapped in human GC remains infectious. In the GC, complement receptors and Fc gamma receptors have been suggested to participate in trapping of HIV; therefore, the relative contribution of complement- and Fc gamma receptors in binding HIV on LT was investigated and the infectivity of this virus was tested. DESIGN: As it is difficult to isolate FDC without contaminations of productively infected cells, HIV was detached from LT of HIV positive individuals using antibodies blocking complement- and Fc gamma receptors. Isolated virus was tested in an infectivity assay. METHODS: HIV detached from LT was quantified by HIV p24 ELISA, PCR and in an in vitro infectivity assay. Presence and accessibility of viral envelope proteins, complement factors and immunoglobulins on the surface of detached viral particles were evaluated through viral capture by respective antibodies. RESULTS: Although both C3d-fragments and IgG molecules were identified on the surface of HIV detached from LT, trapping of HIV was mediated solely by CR2-C3d interactions, whereas contribution of Fc gamma receptors was not detectable. Infectivity assays with HIV stripped from LT of HIV positive individuals revealed that in four out of ten patients HIV particles were infectious. CONCLUSIONS: These findings indicate that in the GC infectious virus is trapped on CR2-expressing FDC (or B cells). Reduction of this pool of HIV could be a therapeutic goal.

Maturation of dendritic cells in the presence of living, apoptotic and necrotic tumour cells derived from squamous cell carcinoma of head and neck.

Dendritic cells (DC) have been recently used as vaccines for stimulation of tumour-specific immunity in various types of cancer. Since data about interactions of DC with tumour cells derived from head and neck cancer are not available, in our study we investigated the effects of head and neck squamous cell carcinoma (HNSCC) cell lines on the maturation of DC. We found that immature DC efficiently internalise necrotic cells, but not living and apoptotic tumour cells. Although apoptotic cells induced a partial maturation of DC, they were not able to stimulate the secretion of IL-12. In contrast, necrotic tumour cell preparations from all three HNSCC cell lines induced the mature phenotype and IL-12 production by DC. Moreover, necrotic cells synergistically augmented stimulatory effects of monocyte-conditioned medium on the maturation of DC. Thus, DC-based vaccination utilizing necrotic tumour cells as a source of tumour antigens, even in combination with inflammatory stimulus, seems to be a suitable strategy for adjuvant immunotherapy in HNSCC.

Pharmacodiagnostic value of the HER family in head and neck squamous cell carcinoma.

Two protooncogene products, EGFR (Her-1, c-erbB-1) and HER2 (Her-2/neu, c-erbB-2), have been reported to be frequently overexpressed in head and neck squamous cell carcinoma (HNSCC). In order to identify patients who may benefit from targeted cancer treatment for these two molecules, we determined the expression status of EGFR and HER2 in 129 HNSCC tumor specimens. Two pharmacodiagnostic kits (EGFR pharmDx and HercepTest) were used to identify HNSCC tumors that overexpress EGFR or HER2. Overexpression of EGFR was detected in 42.6% of the tumor specimens, while HER2 was only rarely expressed (overexpression was observed in just 3.1% of all cases). Given the necessity of new therapeutic modalities for patients suffering from HNSCC, treatment EGFR signaling inhibitors appears to be warranted, whereas therapeutic intervention with HER2 inhibitors seems to be inappropriate in this tumor type.

Phenotypic characterization and distribution of dendritic cells in parotid gland tumors.

Evidence on the relationship between the infiltration of dendritic cells (DCs) and prognosis in head and neck tumors exists. Interestingly, only limited information is available regarding the maturation state and distribution of DCs in parotid gland tumors. The purpose of our study was therefore to extend these observations and to investigate in more detail the density and distribution of mature DCs and Langerhans cells (LCs) in parotid gland tumors. We present immunohistochemical evidence of characterization and distribution of DCs and LCs in parotid gland tumors, enclosed pleomorphic adenomas and malignant parotid tumors. Two populations of mature DCs could be identified, P55(+)-DCs and DC-LAMP(+)-DCs, whereas LCs could be identified as Langerin(+)-LCs. The overall impression was that parotid gland tumors contained only few mature DCs and LCs. Considering the sparsity of mature DCs in the malignant tissues, anti-tumor response can be only limited. On the basis of our data, we imply that the application of DC vaccination in combination with other modalities for treatment of parotid gland carcinoma should be taken into account. In this regard, the utilization of DC immunotherapy for management of minimal residual disease after resection of primary tumor can be promising. Putative targets expressed in this type of tumors have to be defined.

Immunosuppressive effects of soluble factors secreted by head and neck squamous cell carcinoma on dendritic cells and T lymphocytes.

Recent observations suggest that the inability of the immune system to mount an effective immune response against head and neck squamous cell carcinoma (HNSCC) could be a result of the immunosuppression mediated through soluble factors that are secreted by tumour cells. Therefore, we investigated the effects of conditioned medium obtained from cultures of HNSCC cell lines (HNSCC-CM) on the function of dendritic cells (DC) and T cell immune response. In our study, we could not observe any inhibitory effect of HNSCC-CM on the maturation and the cytokine secretion pattern of DC. On the contrary, HNSCC-CM from two of three cell lines consistently decreased the quantity of IFN-gamma- and IL-4-secreting T cells upon restimulation in vitro. In conclusion, our data suggest that soluble factors secreted by HNSCC cells directly inhibit the function of effector T cells, rather than impeding the process of antigen presentation.

Cross-linking of CD32 induces maturation of human monocyte-derived dendritic cells via NF-kappa B signaling pathway.

Dendritic cells (DC) represent a unique set of APCs that initiate immune responses through priming of naive T cells. Maturation of DC is a crucial step during Ag presentation and can be induced by triggering a broad spectrum of DC surface receptors. Although human DC express several receptors for the Fc portion of IgG which were described to play an important role in Ag internalization, little is known about the effects of IgG or immune complexes on DC maturation. In this study, we show that cross-linking of FcgammaR-type II (CD32) with immobilized IgG (imIgG) can induce maturation of human monocyte-derived DC via the NF-kappaB signaling pathway. IgG-mediated maturation was accompanied by a moderate increase of IL-10 secretion, whereas no IL-12 production was observed. Involvement of CD32 was further supported by experiments with the anti-CD32 mAb, which blocked IgG-triggered DC maturation and cytokine secretion significantly. Furthermore, DC cultivated in the presence of imIgG induced allogeneic T cell proliferation. Because this imIgG-induced maturation was considerably impaired in monocyte-derived DC from systemic lupus erythematosus patients, we suggest that DC, which matured in the presence of immune complexes, may contribute to prevention of pathological immune responses.

Importance of the terminal complement components for immune defence against Candida.

Candida activates complement via all three pathways leading to opsonisation and anaphylaxis. The aim of the study was to investigate the influence of the terminal complement system on Candida infections. Thus, fungal cell growth, mitochondrial activity and phagocytosis by polymorphonuclear leukocytes (PMNLs) as well as specific virulence factors, such as release of secreted aspartic protease (Sap) and adherence to epithelial cells, were assessed under the influence of normal or C6/C7-depleted serum. Candida (C.) dubliniensis was used in all experiments as prototype because of its known increased expression of Saps and its strong geno- and phenotypical similarity to the most abundant Candida species C. albicans. Being exposed to sufficient quantities of complement, fungal growth decreased and phagocytosis increased but mitochondrial activities of the yeast increased as well. Concerning the virulence factors, both adhesion and especially Sap release were markedly reduced in the presence of high serum concentrations. Interestingly, at low serum concentrations some opposite effects (an augmented cell growth, a higher Sap release and a stronger adhesion) were observed. In particular, it was shown that the presence of terminal complement factors, and thus the generation of the membrane attack complex, clearly induced a higher fungal mitochondrial activation and has an effect on host defence against yeast cells by augmenting phagocytosis.

Interaction of sertraline with Candida species selectively attenuates fungal virulence in vitro.

This study investigated whether the interaction between isolates of Candida albicans (n=7), Candida parapsilosis (n=3), Candida krusei (n=2), Candida dubliniensis (n=1) and sertraline, a typical selective serotonin reuptake inhibitor, alters candidal virulence. Sertraline treatment of Candida spp. significantly (P<0.05) affected hyphal elongation, phospholipase activity, production of secreted aspartyl proteinases and fungal viability. In addition, monocyte-derived macrophages (MDMs) treated with sertraline reduced inhibition of blastoconidia germination in comparison to MDMs alone. In conclusion, our findings suggest that the interaction between sertraline and Candida spp. may also diminish the virulence properties of this fungal pathogen in vivo.

Complement receptors in HIV infection.

Similar to other pathogens, HIV can directly activate the complement pathway even in the absence of antibodies. During and after seroconversion, HIV-specific antibodies enhance the activation of complement and increase deposition of complement fragments on virions dramatically. However, even in the presence of HIV-specific antibodies, no or only poor lysis occurs. HIV has adapted different protection mechanisms to keep complement activation under the threshold necessary to induce virolysis. In addition to its own envelope proteins, the viral envelope contains membrane-anchored host molecules. Among those are complement regulatory proteins that remain functionally active on the surface of HIV and turn down the complement cascade. In addition, serum proteins with complement regulatory activities become secondarily attached onto the virus, thereby enhancing the protection of HIV against complement-mediated damage. Therefore, opsonised virions accumulate in HIV-infected individuals, which subsequently interact with complement receptor (CR) expressing cells. This review is mainly focused on these interactions, which result either in infection of CR-positive cells with high efficiency, or retention of viral particles on their surface via CRs, thereby promoting transmission of virus to other permissive cells.

Phagocytosis and killing of bacteria by professional phagocytes and dendritic cells.

Dendritic cells (DC) represent a class of professional antigen-presenting cells whose primary function is to alert the immune system, not to clear invading microorganisms. The objective of our study was to compare the abilities of polymorphonuclear neutrophilic leukocytes (PMN), monocytes, monocyte-derived macrophages (MDM), monocyte-derived immature DC (imDC), and mature DC (maDC) to ingest and destroy Staphylococcus aureus and Escherichia coli. Acridine orange staining and fluorescence microscopy demonstrated that MDM, followed by monocytes, imDC, and PMN, internalized bacteria well but that maDC exhibited less pronounced phagocytic activity. PMN, monocytes, and MDM exhibited a much higher capacity to kill ingested bacteria than both imDC and maDC. In summary, these data are in agreement with the generally accepted idea that different types of leukocytes fulfill specialized tasks in antigen presentation and killing of pathogens.